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A view callable in a Pyramid application is typically a simple
Python function that accepts a single parameter named request. A
view callable is assumed to return a response object.

The request object passed to every view that is called as the result of a
route match has an attribute named matchdict that contains the elements
placed into the URL by the pattern of a route statement. For
instance, if a call to pyramid.config.Configurator.add_route() in
__init__.py had the pattern {one}/{two}, and the URL at
http://example.com/foo/bar was invoked, matching this pattern, the
matchdict dictionary attached to the request passed to the view would
have a 'one' key with the value 'foo' and a 'two' key with the
value 'bar'.

The view code in our application will depend on a package which is not a
dependency of the original “tutorial” application. The original “tutorial”
application was generated by the pcreate command; it doesn’t know
about our custom application requirements.

We need to add a dependency on the docutils package to our tutorial
package’s setup.py file by assigning this dependency to the requires parameter in setup().

view_wiki() - Displays the wiki itself. It will answer on the root URL.

view_page() - Displays an individual page.

add_page() - Allows the user to add a page.

edit_page() - Allows the user to edit a page.

We’ll describe each one briefly and show the resulting views.py file
afterward.

Note

There is nothing special about the filename views.py. A project may
have many view callables throughout its codebase in arbitrarily-named
files. Files implementing view callables often have view in their
filenames (or may live in a Python subpackage of your application package
named views), but this is only by convention.

It uses the pyramid.request.Request.route_url() API to construct a
URL to the FrontPage page (e.g. http://localhost:6543/FrontPage), which
is used as the “location” of the HTTPFound response, forming an HTTP redirect.

view_page() is used to display a single page of our
wiki. It renders the ReStructuredText body of a page (stored as
the data attribute of a Page model object) as HTML. Then it substitutes an
HTML anchor for each WikiWord reference in the rendered HTML using a
compiled regular expression.

The check() function is used as the first argument to
wikiwords.sub, indicating that it should be called to provide a value for
each WikiWord match found in the content. If the wiki already contains a
page with the matched WikiWord name, check() generates a view
link to be used as the substitution value and returns it. If the wiki does
not already contain a page with the matched WikiWord name, check()
generates an “add” link as the substitution value and returns it.

As a result, the content variable is now a fully formed bit of HTML
containing various view and add links for WikiWords based on the content of
our current page object.

We then generate an edit URL (because it’s easier to do here than in the
template), and we return a dictionary with a number of arguments. The fact
that view_page() returns a dictionary (as opposed to a response
object) is a cue to Pyramid that it should try to use a renderer
associated with the view configuration to render a template. In our case,
the template which will be rendered will be the templates/view.pt
template, as indicated in the @view_config decorator that is applied to
view_page().

add_page() is invoked when a user clicks on a WikiWord which
isn’t yet represented as a page in the system. The check function
within the view_page view generates URLs to this view.
add_page() also acts as a handler for the form that is generated
when we want to add a page object. The matchdict attribute of the
request passed to the add_page() view will have the values we need
to construct URLs and find model objects.

The matchdict will have a 'pagename' key that matches the name of
the page we’d like to add. If our add view is invoked via,
e.g. http://localhost:6543/add_page/SomeName, the value for
'pagename' in the matchdict will be 'SomeName'.

If the view execution is a result of a form submission (i.e. the expression
'form.submitted'inrequest.params is True), we scrape the page body
from the form data, create a Page object with this page body and the name
taken from matchdict['pagename'], and save it into the database using
DBSession.add. We then redirect back to the view_page view for the
newly created page.

If the view execution is not a result of a form submission (i.e. the
expression 'form.submitted'inrequest.params is False), the view
callable renders a template. To do so, it generates a “save url” which the
template uses as the form post URL during rendering. We’re lazy here, so
we’re going to use the same template (templates/edit.pt) for the add
view as well as the page edit view. To do so we create a dummy Page object
in order to satisfy the edit form’s desire to have some page object
exposed as page. Pyramid will render the template associated
with this view to a response.

edit_page() is invoked when a user clicks the “Edit this
Page” button on the view form. It renders an edit form but it also acts as
the handler for the form it renders. The matchdict attribute of the
request passed to the edit_page view will have a 'pagename' key
matching the name of the page the user wants to edit.

If the view execution is a result of a form submission (i.e. the expression
'form.submitted'inrequest.params is True), the view grabs the
body element of the request parameters and sets it as the data
attribute of the page object. It then redirects to the view_page view
of the wiki page.

If the view execution is not a result of a form submission (i.e. the
expression 'form.submitted'inrequest.params is False), the view
simply renders the edit form, passing the page object and a save_url
which will be used as the action of the generated form.

The view_page, add_page and edit_page views that we’ve added
reference a template. Each template is a ChameleonZPT
template. These templates will live in the templates directory of our
tutorial package. Chameleon templates must have a .pt extension to be
recognized as such.

This template is used by view_page() for displaying a single
wiki page. It includes:

A div element that is replaced with the content
value provided by the view (rows 45-47). content
contains HTML, so the structure keyword is used
to prevent escaping it (i.e. changing “>” to “&gt;”, etc.)

A link that points
at the “edit” URL which invokes the edit_page view for
the page being viewed (rows 49-51).

This template is used by add_page() and edit_page() for adding
and editing a wiki page. It displays
a page containing a form that includes:

A 10 row by 60 column textarea field named body that is filled
with any existing page data when it is rendered (rows 46-47).

A submit button that has the name form.submitted (row 48).

The form POSTs back to the “save_url” argument supplied
by the view (row 45). The view will use the body and
form.submitted values.

Note

Our templates use a request object that
none of our tutorial views return in their dictionary.
request is one of several
names that are available “by default” in a template when a template
renderer is used. See *.pt or *.txt: Chameleon Template Renderers for
information about other names that are available by default
when a Chameleon template is used as a renderer.

Our templates name a single static asset named pylons.css. We don’t need
to create this file within our package’s static directory because it was
provided at the time we created the project. This file is a little too long
to replicate within the body of this guide, however it is available online.

This CSS file will be accessed via
e.g. http://localhost:6543/static/pylons.css by virtue of the call to
add_static_view directive we’ve made in the __init__.py file. Any
number and type of static assets can be placed in this directory (or
subdirectories) and are just referred to by URL or by using the convenience
method static_url
e.g. request.static_url('{{package}}:static/foo.css') within templates.

The __init__.py file contains
pyramid.config.Configurator.add_route() calls which serve to add routes
to our application. First, we’ll get rid of the existing route created by
the template using the name 'home'. It’s only an example and isn’t
relevant to our application.

We then need to add four calls to add_route. Note that the ordering of
these declarations is very important. route declarations are matched in
the order they’re found in the __init__.py file.

Add a declaration which maps the pattern / (signifying the root URL)
to the route named view_wiki. It maps to our view_wiki view
callable by virtue of the @view_config attached to the view_wiki
view function indicating route_name='view_wiki'.

Add a declaration which maps the pattern /{pagename} to the route named
view_page. This is the regular view for a page. It maps
to our view_page view callable by virtue of the @view_config
attached to the view_page view function indicating
route_name='view_page'.

Add a declaration which maps the pattern /add_page/{pagename} to the
route named add_page. This is the add view for a new page. It maps
to our add_page view callable by virtue of the @view_config
attached to the add_page view function indicating
route_name='add_page'.

Add a declaration which maps the pattern /{pagename}/edit_page to the
route named edit_page. This is the edit view for a page. It maps
to our edit_page view callable by virtue of the @view_config
attached to the edit_page view function indicating
route_name='edit_page'.

As a result of our edits, the __init__.py file should look
something like:

We can finally examine our application in a browser (See
Starting the Application). Launch a browser and visit
each of the following URLs, check that the result is as expected:

http://localhost:6543 in a browser invokes the
view_wiki view. This always redirects to the view_page view
of the FrontPage page object.

http://localhost:6543/FrontPage in a browser invokes
the view_page view of the front page object.

http://localhost:6543/FrontPage/edit_page in a browser
invokes the edit view for the front page object.

http://localhost:6543/add_page/SomePageName in a
browser invokes the add view for a page.

To generate an error, visit http://localhost:6543/foobars/edit_page which
will generate a NoResultFound:Norowwasfoundforone() error.
You’ll see an interactive traceback facility provided
by pyramid_debugtoolbar.